Purpose: To compare the early clinical outcomes between anesthetic techniques in outpatient unicompartmental knee arthroplasty (UKA) and investigate factors responsible for delayed discharge. Method: A randomized controlled trial was conducted on 64 consecutive and unselected patients who underwent primary, medial UKA and randomly divided into two groups:32 patients with spinal anaesthesia(Group A) and 32 with general anaesthesia(Group B). There were no significant differences in gender, age, body mass index (BMI), the hospital for Special Surgery knee score (HSS), and American Society of Anesthesiology(ASA) class between the two groups (P >0.05).Results:Totally 64 patients were involved, including 20 males and 42 females, with an average age of 60.4 ± 3.8 year-old. The length of stay(LOS) and total expense were significantly less in group A than those in group B (P < 0.05). There was no significant difference between two groups on the discharge day and the reasons for not discharge(P>0.05). Lack of mobilization (84%), pain (23%), and PONV (17%) were main reasons for patients not meeting the discharge criteria on DOS (Table 2). Patients with spinal anaesthesia underwent a longer surgery time than those with GA.(P<0.05); Patients in the Group A had a significantly earlier oral fluid intake and walking unaided(P<0.05); Pain occurred significantly earlier in Group B(P<0.05). Conclusion: In patients who underwent outpatient UKA, spinal anaesthesia is significantly superior to general anaesthesia with shorter discharge time and lower cost. With strict patient selection and safe anaesthesia, outpatient UKA could attain a good clinical outcome with both anaesthesia techniques.